


Private Beach

by Mercy_Run



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap, Dirty Talk, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Fluff, Horrible Puns, M/M, Mating Cycles/In Heat, Praise Kink, Semi-Public Sex, Smut
Language: English
Status: Completed
Published: 2017-09-17
Updated: 2017-09-17
Packaged: 2018-12-31 00:25:16
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,130
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12120555
Author URL: https://archiveofourown.org/users/Mercy_Run/pseuds/Mercy_Run
Summary: The Underswap brothers share an intimate moment together on a date gone array.  Papyrus can't have his Magnificent sibling blame himself for getting them lost.





	Private Beach

**Author's Note:**

> For Peeptheram from my 500 Follower Celebration WAAAAAY BACK on Tumblr. <3
> 
> NSFW Blog: mercy-run.tumblr.com

Papyrus dozed slightly on the couch in their apartment with his orange hoodie tugged over his skull, snapping awake at intervals to check if Sans had finished getting ready. They had been on the surface for over a year now and the lanky skeleton was just coming to terms that this may be permanent. He hoped this was the last reset because he didn’t think he could bear losing this timeline. The first timeline where his little brother had confessed his love.

Chara has promised, after all.

Worrying the toothpick wedged in between his teeth, Papyrus reckoned that now that he knew Sans had those feelings, picking up their relationship again would be easy. There would be no guilt, no hesitation or awkwardness.

But still…

If the skeleton had to start over and over again, he feared that his apathy from the timelines might bleed over into his love for Sans.

Papyrus wouldn’t stand for that.

“PAPY, YOU ARE LOST IN YOUR OWN HEAD AGAIN!”

The lazy skeleton startled and regarded his smaller brother with an amused tilt of his teeth. Sans had changed out of his soft grey ‘battle body’ and blue neckerchief in favor of a navy short sleeved turtle-neck and coal colored pants. He had to admit, his younger brother was quite the sharp dresser lately.

Probably something to do with Hapstablook and Undyne…

“what can i say, bro? my skull is rather-”

“STOP!” Sans stamped his foot on the floor and sent him a stern look, “ONE PUN FROM YOU TONIGHT AND I WILL CHANGE MY MIND ABOUT THIS DATE!”

“wow, bro. harsh. it was your idea to begin with, after all,” Papyrus grinned as the small skeleton blushed an adorable blue. Sans crossed his arms over his chest stubbornly and glanced to the side.

“THAT IS BESIDE THE POINT BROTHER AND YOU KNOW THAT!” The younger monster objected and Papyrus chuckled, standing to his full height and stretching; the resulting popping bones causing Sans to blush even harder.

“welp, where are we heading anyways?” The tall skeleton questioned with an indulgent smile. Sans gave him a slow once-over.

“I GUESS IT IS A MOOT POINT TO ASK YOU TO DRESS MORE PRESENTABLY.”

Papyrus was suddenly unsure.

“does what you have in mind have a fancy dress code or something?” He questioned and Sans immediately picked up on his older brother’s discomfort. He beamed up at Papyrus and shook his head.

“YOU ARE FINE AS IS, AS MUCH AS I DISAGREE WITH YOUR FASHION SENSE!” The smaller skeleton replied, assuring his sibling. Papyrus’ gaze softened.

“you make up for that, bro. you look wonderful.”

Sans’ smile widened and his pupils turned to stars, “THANK YOU, PAPY! SHALL WE GET GOING, THEN?”

“you still haven’t said where we are goi-”

“IT ISN’T SOMEWHERE WE HAVE BEEN, SO WE WILL HAVE TO WALK. ALPHYS TOLD ME ABOUT THIS PLACE DOWNTOWN AND HER DIRECTIONS SHOULD BE EASY TO FOLLOW!” Sans insisted and Papyrus nodded, chewing idly on the toothpick as Sans opened the door.

“lead on, blueberry.” The taller skeleton murmured fondly and they both set out into the brisk nighttime air.

Riding on Sans’ motorcycle was not Papyrus’ preferred mode of transport but he managed to not jostle his smaller brother as the passenger. The older brother had once tried to get Sans to buy a side car and the smaller monster immediately turned it down, swearing it would not 'be cool.’

At least Papyrus got him to wear a helmet…

Downtown Ebbot City was still crowded this time of night; the bar life and entertainment preventing the streets from becoming empty until the wee hours of the morning. They still drew looks, most were curious and a few were enough to have Papyrus extremely vigilant. Them surfacing hadn’t changed the core nature of most humans.

After an hour of walking, Sans frowned at the written instructions Alphys had provided. It was obvious that they were lost, but the taller brother didn’t mind. He didn’t particularly want to point out any faults in the Captain because Sans was protective of his friends.

“THIS WAY!” Sans called back to him and they ended up closer to the edge of the city than where this mysterious date location was. Sans’ normally confident strides had become a slump and Papyrus saw a slight tremor in those small shoulders.

Ah, no. This wouldn’t do.

He couldn’t have his baby brother upset, especially since Sans had been so excited planning this date for the both of them. The skeleton chased his thoughts a bit before the faint lap of water caught his attention.

“hey, bro.”

Sans startled but didn’t turn to face him.

“Y-YES, PAPYRUS!?”

Sans didn’t want him to know he was in tears.

“you hear that?” Papyrus prompted gently.

His small brother halted mid-step and hesitated before he whirled around to face Papyrus, grinning excitedly despite there being tears pooling in his eye sockets.

“IT SOUNDS LIKE WATER NEARBY!” He pointed out before frowning and taking in their surroundings, “I HADN’T REALIZED…”

Unwilling to allow Sans to drop back into his low mood, he spoke up, “it’s probably the beach, bro. i would say that is more romantic than anything else, yeah?”

Sans’ grin widened and he closed the distance between them, snatching Papyrus’ larger hand.

“THEN WE SHALL SPEND SOME TIME THERE! ONLY THE BEST FOR MY PAPY!”

Papyrus grinned to himself as Sans tugged him over the partition.

His little brother was so cute…

“Wow…”

The taller skeleton blinked his eye sockets at the hushed tone Sans had adopted and he soon found out why. There wasn’t a single cloud to block out the vast array of stars spilled across the inky night sky. Where the horizon touched the water of the ocean was nearly indescribable.

It was breathtaking.

He tore his attention from the sky to take in the small strip of sand they had discovered. It was probably only enough for two people to lay down at best and had overgrowth.

It felt cut away from the rest of the city.

“THIS IS A PERFECT SPOT!” Sans concluded, plopping down in the sand, “THIS IS NOW OUR SECRET BEACH!”

Calling it a beach was generous, but the taller skeleton felt his soul hum happily at the sentiment. Exploring new things was something that had came with surfacing. Papyrus lowered himself on the sand, his spine pressed up against the cement partition. He held his arms out for Sans, who happily scrambled into his embrace.

They both quietly took in the scenery, expressions soft.

The pain… The resets…

If Papyrus could come back here, they were worth it…

“Papy…?”

He hummed at Sans’ gentle call of his nickname.

“I’m glad we got lost.”

Papyrus blinked and looked down at his little brother, discovering a wry smile pulling the other’s teeth up. He huffed out a breath, amused.

“sometimes the best things aren’t planned,” the hoodie-clad skeleton murmured and Sans blinked, pupils winking into stars.

“THAT WAS DEEP, ESPECIALLY FOR YOU!”

“i’m not always a numb-skull, bro.”

“PAPY!” Sans puffed out his cheeks before grinning once more, turning in his older brother’s embrace. Papyrus’ large hands fell to Sans’ small hips, his thumb idly smoothing over the pelvic arch peeking through the fabric. He smiled upon finding those starry pupils searching his face, his younger brother’s skull flushed a soft blue.

He chuckled.

“really, blueberry. here?” Papyrus questioned and his baby brother made a soft frustrated noise.

“No one will see so it isn’t THAT lewd…” Sans murmured, “besides…it is rather romantic.”

The taller skeleton made a soft considering noise before hiking up the turtle-neck and grinning at the blue magic shining from the other’s clothed pelvis. Sans whimpered softly as Papyrus shifted his thigh to grind into the apex of his tiny brother’s hips.

“oh? how long have you been wanting this, lil’ berry?” He purred, sliding his orange ecto-tongue against sharpened fangs.

“L-long enou-ooohhhh…” Sans’ blue tongue lolled out between parted teeth as Papyrus forced his hips down in a harsh grind.

“you’re already wet, sans. i can feel it through all these clothes,” he hummed lowly, “you poor thing…”

Sans was already putty in his hands. Papyrus knew that the smaller skeleton was weak for dirty talk, even if the other would deny it from the underground to the Surface.

“Papy…” Tears were gathering in the corners of Sans’ eye sockets, blue eye-lights blown wide, “please, Papy…please…”

Papyrus made a low sympathetic noise in his rib cage.

“my poor baby brother,” the taller skeleton cooed, “you’re so tense and soaking wet. let’s get you out of these pants, hm?”

“Oh yes, please,” Sans responded, trembling as he shifted in Papyrus’ grip so that his pants could be pulled off more easily. The other’s blue magic had formed a small blue cunt that was oozing steadily. Sans’ clit was already swollen, more than ready.

Papyrus was one to tease often, especially during sex but Sans was already shaking and whining softly in need.

“shhhh,” he hushed, laying his small brother back against the sand, “no teasing this time, i promise.”

“Papy…” The other’s bones were trembling and Papyrus hissed through his teeth as the faintest smell of the other’s heat registered.

“awww, baby, why didn’t you tell me your cycle was due?” The larger skeleton lowered the zipper of his cargo pants, his own orange magic forming eagerly at the scent.

“Didn’t w-want you t-to think you had to to…”

“sans, i love you. i don’t 'have to’, i 'want to’. now spread your legs, sweetheart,” Papyrus murmured, settling in between the smaller skeleton’s quivering femurs. Gripping his orange shaft, Papyrus shuddered as he teased open the wet glowing lips before lifting one of Sans’ legs up to get the angle he knew his brother adored. Papyrus slowly hilted himself, the skeleton below him crying out as he was stretched, the head of the other’s dick striking the back of his magic.

“PAPY-” Sans mewled and the older skeleton snapped his hips back before slamming home.

The resulting scream was worth it.

“that’s it, sans…” He moaned, feeling the other’s cunt clench reflexively around his throbbing shaft. The smaller monster was writhing underneath him as Papyrus set up a punishing pace.

“so fucking good,” Papyrus moaned, the sloppy sounds of their joined magic driving him wild, “that’s-that’s right, take all of it…”

The fluttering of Sans’ walls as well as his increasingly desperate cries egged the larger monster on.

“you gonna cum, huh?” He thrust as deeply as he could go before grinding their magic briefly in between thrusts, “that’s right, sans. cum all over your older brother’s big cock, yeah?”

Sans wailed, his pussy clamping around Papyrus’ driving cock. Blue magic splashed against his pelvic bone but the taller skeleton didn’t stop, fucking his small brother right through his orgasm.

His younger sibling felt heavenly, oversensitive and subconsciously trying to force his length out; blue eye-lights rolled up. Papyrus grinned and thumbed the clit mercilessly, feeling it throb under his attentions.

“PAPY- I CAN’T-!” Sans wailed but Papyrus shushed him, pressing their teeth together and tangling tongues.

“come on, baby bro,” he murmured, lowering his hands to Sans’ small hips and forcing him down onto his shaft, “you’re doing so good. make me cum like a good boy.”

“OH STARS, PAPYRUS!” Sans was nearly delirious, climbing towards a second peak but the smaller skeleton made a conscious effort to clench his magic tight, just like he knew Papyrus enjoyed.

“Yessss,” the taller skeleton hissed encouragingly, angling Sans to go as deep as possible, “i’m so fucking close. so close.”

“Hah, Papy~!” Sans tongue lolled and Papyrus smirked, his pace now a brutal thing as he chased his own pleasure.

“where do you want it, little brother?” He panted, thrusting harshly, “fuck…i’m gonna-”

“INSIDE! COME INSIDE, PAPYRUS!” Sans wailed and Papyrus growled lowly in his rib cage as he felt his smaller sibling clench around him as he found his second release that night. He thrust once and twice more before moaning lowly as he spilled his magic deep into Sans, their magic dripping onto the sand and mixing.

They both spent a few long minutes catching their breath. The smell of Sans heat was getting richer and stronger.

Papyrus twitched deep inside Sans, causing the smaller monster to moan.

“we’re…going to be here awhile…” The older brother panted and Sans murmured a soft agreement.

“next time, tell me if you are in heat, baby,” Papyrus looked down at his wreaked sibling, “i don’t mind 'helping’ out. no need for romance.”

Sans smiled up at him, shifting his small hips to bury Papyrus deeper as he panted.

“A-Again?”

Papyrus smirked, “you know it.”


End file.
